In general, a joint functions to transmit rotational power (torque) between two rotation shafts which meet each other at an angle. In the case of a propeller shaft having a small power transmission angle, a Hooke's joint, a flexible joint, etc. are used, and in the case of the driving shaft of a front wheel drive vehicle having a large power transmission angle, a constant velocity joint is used.
Since the constant velocity joint can reliably transmit power at a constant velocity even when an angle between a driving shaft and a driven shaft is large, the constant velocity joint is mainly used for the axle shaft of an independent suspension type front wheel drive vehicle. When viewed from a shaft, a tripod type constant velocity joint is provided to one end of the shaft which faces an engine (i.e., the inboard-side end), and a ball type joint is provided to the other end of the shaft which faces a tire (i.e., the outboard-side end).
FIG. 1 is a cross-sectional view illustrating a general sliding constant velocity joint for a vehicle.
As illustrated in FIG. 1, the general sliding constant velocity joint for a vehicle includes an outer race 2 which rotates by receiving rotational power of the engine (not shown) and is defined with grooves as track grooves 21 on the inner surface thereof, an inner race 3 installed in the outer race 2, a plurality of balls 4 for transmitting the rotational power of the outer race 2 to the inner race 3, and a cage 5 for supporting the balls 4.
The outer race 2 has a track groove 21 parallel with the center axis and an inner surface 22 of a cylinder having an inner diameter do.
The inner race 3 has a track groove 31 parallel with a central axle and an outer diameter 32 of a sphere having an outer diameter di.
In general, the balls 4 include six or eight balls and have the same pitch circle diameter (PCD) and the same size.
The cage 5 has a spherical outer surface 51 having a spherical portion and a linear portion, a spherical inner surface 52 having a spherical portion, and a window grinding surface 53 by which the balls 4 are restrained.
The center Oi of the inner diameter of the cage 5 and the center Oo of the outer diameter of the cage 5 are symmetrically spaced an axial offset amount f apart from each other in view of a plane W passing the joint center O.
The operation of the general sliding ball type constant velocity joint for a vehicle constructed as mentioned above will now be described.
As the rotational power outputted from an engine (not shown) is transmitted to the shaft 1 through a transmission (not shown) and then transmitted to the inner race 3 through the outer race 2 and the ball 4, so that a wheel (not shown) is rotated.
The balls 4, which are restrained by the window grinding surface 53 of the cage 5 and are also restrained between the track groove 21 of the outer race 2 and the track groove 31 of the inner race 3, transmit rotational torque. In this case, the spherical inner surface 52 of the cage 5 restrains the spherical outer surface 32 of the inner race 3, and the window grinding surface 53 of the cage 5 restrains the balls 4, thereby enabling axial sliding and articulated joint movement. When the joint is articulated, the balls 4 are always positioned on the plane W to then rotate by half of the joint angle together with the cage 5.
Therefore, as the balls 4 slidably move in the track groove 21 of the outer race 2, the joint is articulated to follow the displacement of the vehicle.
However, the conventional sliding ball type constant velocity joint is configured such that axial power transmitted to the axially moving inner race 3 is transmitted to the inner spherical surface 52 of the cage 5 through the outer spherical surface 32 of the inner race 3 to push the balls 4. That is to say, the inner race 3, the cage 5, and the balls 4 are subunits, which move in the same axial direction at the same time, may not absorb idle vibration generated from the vehicle during idling but may transmit the same to a vehicle body.